Coating composition comprising paraffin wax and microcrystalline wax



United States Patent 2,885,340 .co {G ,coivifPo f'I'twN CbMlRISINGIARAFFiN WAX AND MICROCRYSTALLINE WAX John D. T'ench, Prospect Park, :Pa, assi'gnor to sun on Company, Philadelphia, 'Pa., a corporation of New Jersey No brewing. Application April 21, 1955 Serial No. 504,366

2 Claims. (Cl. 208*21) A l his invention relates to a novel wax composition. More particularly, the invention relates to a novel 'c'om- {position containing a major proportion of specific pertain wax and a minor proportion of a sp ecificmic'rocrystalline wax, the composition being especially suitable for coating fibrous sheets and containers for packaging.

ULS. 'Pate'n't No. 2,624,501 describes and claims a pafaiiin having specific pro'perties which is especially suitable for coating 'fibrous sheet materials and containers such as milk containers. The claimed'paraffin wax has a fiieltingpoint of from 125 to 132 F. and atensile strength at 40 F. of from 275 psi. to 325 p.s .i., the tensile strength at 40 F. being at least 25 psi. higher than the tensile strength at 70 F. An advantage stated for-this wax-isthat it is unnecessary to'compoun'dtherewith foreign materials in order to obtain good coatings with the wax. Actual commercial use, however, has disclosed certain disadvantages of coatings formed from this wax. Such coatingson'fibrous sheet materials may develop minute'imperfections which impart aserpentine elfect to the coating thereby creating an unsightly .appearance, and leakage of packaged liquid materials "through the imperfections may develop. 'Another dis- 'advantag'e of the wax is that it must be'packaged for "shipment in small lots to prevent blocking-of the slabs *of -waxyie, to'prev'entiusion of stacked wax slabs into a large, single mass.

:The development of the serpentine efiecvcan be .partially controlled by close regulation of the temperature of the wax'atthe time of coating the fibrous-sheet, the time 'usedfor coating thissheet, -e.-g., the time of-immer- 'Sion'of the fibrous sheet material in a molten wax bath, therate and means of cooling of the resulting coated product, the, type of=fibrous sheet material coated and thedesign ofthe coating-equipment. Close-regulation of these variables, however, incommercialiuseage is 'not .practical. The blocking of wax slabs can be prevented only by packaging the wax slabs in-srnall lots, andby providing a barrier, such as apaper sheet, between the wax slabs. This, however, requires individual handling and hence is inexpensive both'in. packaging the Wax and in its subsequent use. i

An object of thepresent invention is'to provide a wax composition especially-suitable for coating fibrous ysheet materials such as fluid containers. Another object isto provide-a wax composition having substantially the properties of the parafiin wax described in said Patent No. 2,624,501 which, when applied as'a coating on fibrous materials, does not develop minute imperfections imparting a serpentine 'eifect to'the coating. A- further object is to provide a wax composition having substan- .tially the properties of the parafiin wax of said Patent No. 2,62 4 ,501which does not block when slabs formed therefrom are stacked.

It has nowbeen found that by incorporating abo'ut2% by weight-of a specific hi icrocrys'talline'wax, as described hereinafter, in the paraifid'wax' of said Patent No.

ice

2 2,624,501, the properties of the resulting wax composition are substantially the same as the properties of the parafiin wax, the resulting 'wax composition does not develop a serpentine eifect when used for coating fibrous materials, and the wax composition does not block when slabs thereof are in stacked relationship.

It is essential to the successful preparation of "the composition of the invention that the microcrys'talline Wax employed have specific properties. The microci'ystalline wax must have a melting point of from 185 F. to 200 F. (ASTM D127 -49), a viscosity of from '81 to 89 SU S at 210 F. (D446-53), a refractive index 2 of 1.435 tofl.43 8, a penetration of from 30 to 65 at 160 F. (ASTM 135-52), and a penetration of not above 5 at 77 F. (ASTM 'D5-52). The molecular weight of the microcrystalline wax is approximately 650. A microcrystalline wax which does not have properties within the'stated "ranges doesnot give a satisfactory wax composition when incorporated in the parafiin wait of Patent No. 2,624,501.

The microcrys'talline wax of the invention is prepared from petroleum. Slack wax fromthe dewaxing of lubri- "cating oil is subjected to vacuum distillation and the material boiling below about 490 F., and preferably below 525 F.,-at"2 mm. of mercury pressure-is separated. The residual fractionis used toprepare the microcrystalline wax 'ofthe present wax-composition. The residual fraction is dissolved in a isolvent,'such as a'mixture of methyl'ethyl ketone and benzene, at-anelevated :tem-

perature. The wax solution is' -then cooled' to'atemperw ture of'from about 95 'to .1l0 F. and the wax precipitated 1 at this temperature separated such as by filtering. The resulting wax is the microcrystalline wax=used in preparing the present composition. It will *berunderstood that other solvents such as "ethylene dichloride,

toluene, and the likeymaybe employedfor the dissolutionofthe Wax atan elevated temperature. Substitution of such materials-in wholeor in part for 'the benzene and/ or the methyl ethyl ketone may require an adjustment of the temperature. ofiprecipitatiomit being necessary that eating oils,- and which contains about 30% oil, is subjectedto vacuum distillation and a distillate fraction boil- --ing between about 325 F. and 650 F. at 10 mm. -of mercury pressure is separated. This fraction is-dissolved in a solvent, preferably a a mixture of methyl ethyl ketone and' benzene in about equal volumes, dissolution being at a temperature of from-about 165 -F. to 1-95 F. The

solution is slowly cooled to a temperatureof'f1om ".F. "to F., and the precipitated wax separated, suchas'by filtering or centrifuging. "The resulting filtrate is further cooled to a temperature of from 25 F. to 30F., andthe precipitated filtered. This latter filtered wax, on further treatment, forms the-paraffin wax -componentof the-wax-c'omposition of-- the present invention. It is .preferred to wash the wax cake, either by washing the filter cake or by repulping and subsequent filtration, using as the washing material the solvent employed in the dissoludoubt the "wax. Also, the washing operation ispreferably "conducted at a temperature approximating the temperature of the "final precipitation. v As above stated-it is essential thatan amount of *microcrystalline wax of about 2% by weight be incorporated in the paraflin wax. The amount of microcrystalline wax incorporated must always be within the range of from 1.4% to 2.6% by weight. A composition having components outside of this range does not give satisfactory results as shown hereinafter by example.

The incorporation of the microcrystalline wax in the parafiin wax may be by any convenient means such as by admixing the waxes in the molten state to obtain a homogeneous blend. The incorporation of the required quantity of microcrystalline wax in the paraffin wax does not deleteriously afiect or even substantially change most of the properties, such as melting point and flexibility, of the paraffin wax which render it especially suitable for coating fibrous materials. However, the tensile strength is somewhat increased thereby enhancing the value of the wax compositions for coating purposes. Generally the tensile strength at 40 F. will be from about 350 to 450 p.s.i., and the tensile strength at 40 F. will be at least 25 p.s.i. higher than the value obtained at 70 F.

The following examples illustrate compositions of the invention:

Example I A wax composition according to the invention was prepared by incorporating 2% by weight of a microcrystalline wax in a paraffin wax. The microcrystalline wax was prepared by vacuum distilling slack wax from the dewaxing of lubricating oil to remove the components thereof boiling below about 525 F. at 2 mm. of mercury pressure. The residual fraction was dissolved in a solvent, consisting of a mixture of methyl ethyl ketone in about equal parts, at an elevated temperature. The resulting solution was then cooled to a temperature of about 105 F. and the wax precipitated at this temperature separated by filtration. The wax cake was washed with additional solvent and solvent removed from the washed cake by evaporation.

The resulting microcrystalline wax had a melting point of about 192 F., a viscosity of about 86 SUS at 210 F., a penetration of about 47 at 160 F. and about 3 at 77 F., a refractive index (n of about 1.4363, and a molecular weight of about 650.

The parafiin wax was prepared as described in Patent No. 2,624,501, and had a melting point of about 127 F., a tensile strength of about 250 at 70 F. and of about 280 at 40 F.

The composition was prepared by adding 2% by weight of the microcrystalline wax, in the molten state, to the paraflin wax, also in the molten state, with agitation to secure a homogeneous blend on cooling.

The properties of the paraffin wax and of the wax composition of the invention were as follows:

As shown by the data, the physical properties of the wax composition of the invention are substantially the same as of the parafiin wax, except that the tensile strength is increased.

Example 2 The parafl'in wax component of the composition of the invention and compositions prepared by incorporating various amounts of the microcrystalline wax of Example 1 therein, when used to coat fibrous sheet materials, such as milk container cartons, and when slabs thereof are stacked, give the following results:

Parafiin waxgives serpentine effect and blocks.

Parafiin wax /2% microcrystalline waxgives serpentine effect and blocks.

Paraflin wax +1% microcrystalline waxblocks.

Parafiin wax +2% microcrystalline waxdoes not give serpentine effect or block.

Paraflin wax +3% microcrystalline wax-wax coating flakes from the fibrous sheet.

In this example, 175 wax slabs, each about 19 inches by 12 inches by 1% inches, having a total weight of about 1750 pounds, are stacked to form substantially a cube. The slabs formed from the wax composition having 2% by weight microcrystalline wax did not block even when stored for long times at ambient temperature, whereas wax compositions having less than about 2% by weight, and specifically less than about 1.4% by weight of the microcrystalline wax, when so stacked fuse into what is essentially a single wax mass.

Example 3 Wax compositions similar to the wax compositions of the invention were prepared in which microcrystalline waxes other than the required microcrystalline wax of the invention were used.

A wax composition was prepared consisting of the paraflin wax of Example 1 and 2% by weight of a microcrystalline wax having a melting point of 178 F., a penetration of 12 at 77 F., and a viscosity of 73 SUS at 210 F., the test methods being as herein designated for the microcrystalline wax of the invention. Wax slabs prepared from this composition could not be stacked, as described in Example 2, without blocking, i.e., without adhesion of the slabs to each other.

Another wax composition was prepared consisting of the paraffin wax of Example 1 and 2% by weight of a microcrystalline wax having a melting point of F., a penetration of 22 at 77 F., and a viscosity of 87 SUS at 210 F., the test methods being as herein designated for the microcrystalline wax of the invention. Wax slabs prepared from this composition could not be stacked, as described in Example 2, without blocking.

As shown by the foregoing examples, the properties of the microcrystalline wax component of the wax composition of the invention must be within the limits herein described, and the quantity of this wax incorporated in the parafin wax must be about 2% by weight. When microcrystalline waxes having properties outside of the required limits are used, the resulting wax composition does not meet the requirements for the wax compositon of the invention, and when a quantity of the microcrystalline wax component of the wax composition of the invention is varied from about 2% by weight, as herein described, the resulting wax compositions do not meet the requirements for the wax composition of the invention.

The invention claimed is:

1. A wax composition consisting essentially of a hydrocarbon paraflin wax derived from petroleum and having a melting point of from 125 F. to 132 F., a tensile strength at 40 F. of from 275 p.s.i. to 325 p.s.i., the tensile strength at 40 F. being at least 25 p.s.i. higher than the tensile strength at 70 F., and from 1.4% to 2.6% by weight of a microcrystalline wax derived from petroleum and having a melting point of from 185 F. to 200 F., a viscosity of from 81 to 89 SUS at 210 F., a refractive index (n of from 1.435 to 1.438, apenetration of from 30 to 65 at F., and a penetration of not above 5 at 77 F.

2. A wax composition according to claim 1, said wax composition having a melting point of from 125 F. to 132 F. and a tensile strength at 40 F. of from 350 6 Abrams et a1 May 9, 1944 Adams et a1. Oct. 31, 1944 Ferris Jan. 6, 1953 Hunter et al Feb. 23, 954 Padgett Feb. 26, 1957 OTHER REFERENCES Technical Association Pulp and Paper Industry Bulletin No. 27, March 13, 1944, page 1 relied on. 

1. A WAX COMPOSITION CONSISTING ESSENTIALLY OF A HYDROCARBON PARAFFIN WAX DERIVED FROM PETROLEUM AND HAVING A MELTING POINT OF FROM 125* F. TO 132* F., A TENSILE STRENGTH AT 40 F. OF FROM 275 P.S.I.THE TENSILE STRENGTH AT 40* F. BEING AT LEAST 25 P.S.I. HIGHER THAN THE TENSILE STRENGTH AT 7O F,. AND FROM 1.4% TO 2.6% BY WEIGHT OF A MICROCRYSTALLINE WAX DERRIVED FROM PETROLEUM AND HAVING A MELTING POINT OF FROM 185* F., TO 200* F., A VISCOSITY OF FROM 81 TO 89 SUS AT 210* F., A RECFRACTIVE INDEX (ND212) OF FROM 1.435 TO 1.438. A PENETRATION OF FROM 30 TO 65 AT 160* F., AND A PENETRATION OF NOT ABOVE 5 AT 77* F. 